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REFERENCE COPY FOR LIBRARY USE ONLY WILD HORSE POPULATIONS: >i FIELD STUDIES IN GENETICS AND FERTILITY Report to the Bureau of Land Management U.S. Department of the Interior Committee on Wild Horse and Burro Research Board on Agriculture National Research Council - NATIONAL ACADEMY PRESS Washington, D.C. 1991
73? NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Frank Press is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Samuel O. Thier is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Frank Press and Dr. Robert M. White are chairman and vice-chairman, respectively, of the National Research Council. This project was supported by the Bureau of Land Management, U.S. Department of the Interior, under contract no. AA852-CT5-11. Available from: Board on Agriculture National Research Council 2101 Constitution Avenue, N.W. Washington, D.C. 20418 Printed in the United States of America
COMMITTEE ON WILD HORSE AND BURRO RESEARCH FREDERIC H. WAGNER, Chair, Utah State University JOEL BERGER, University of Nevada DALE R. McCULLOUGH, University of California, Berkeley JOHN W. MENKE, University of California, Davis EDWARD S. MURRAY, Spur Veterinary Hospital, Spur, Texas BILL W. P1CKETT, Colorado State University ULYSSES S. SEAL, Veteran's Administration Medical Center, Minneapolis, Minnesota MAITLAND SHARPE, Izaak Walton League of America, Arlington, Virginia Staff RICHARD WILES, Project Officer AMY GORENA, Senior Project Assistant ui
BOARD ON AGRICULTURE THEODORE L. HULLAR, Chair, University of California, Davis PHILIP H. ABELSON, American Association for the Advancement of Science C. EUGENE ALLEN, University of Minnesota DALE E. BAUMAN, Cornell University R. JAMES COOK, Agricultural Research Service at Washington State University ELLIS B. COWLING, North Carolina State University ROBERT M. GOODMAN, Visiting Professor, University of Wisconsin, and National Research Council, Scholar-in-Residence TIMOTHY M. HAMMONDS, Food Marketing Institute PAUL W. JOHNSON, Iowa State House of Representatives NEAL A. JORGENSEN, University of Wisconsin ALLEN V. KNEESE, Resources for the Future JOHN W. MELLOR, International Food Policy Research Institute ROBERT L. THOMPSON, Purdue University JAN VAN SCHILFGAARDE, U.S. Department of Agriculture, Fort Collins, Colorado ANNE M. K. VIDAVER, University of Nebraska CONRAD J. WEISER, Oregon State University Staff CHARLES M. BENBROOK, Executive Director* JAMES E. TAVARES, Acting Executive Director ROBERT M. GOODMAN, NRC Scholar-in-Residence CARLA CARLSON, Director of Communications BARBARA RICE, Editor "Through November 1990. IV
Preface When Congress passed the Wild Free-Roaming Horse and Burro Act (P.L. 92-195) in 1971, it decreed that the secretaries of interior and agricul- ture are to engage in the "protection, management, and control of wild free- roaming horses and burros on public lands . . . [thenceforth] to be consid- ered ... as an integral part of the natural system" on those lands (U.S. Congress, 1971). The public lands referred to are those under the adminis- tration of the Bureau of Land Management (BLM) and the Forest Service. Most horses and burros are on land administered by BLM, and most of the management responsibility rests with this agency. To casual travelers through the arid and semiarid lands of the western United States, there may seem to be little human land use and ample room for these equine "living symbols of the historic and pioneering spirit of the West." But in fact diverse interest groups demand an array of competing, often conflicting, uses of these lands: mining, timber harvesting, domestic livestock grazing, consumptive and nonconsumptive wildlife uses, recreation, water harvest, and energy production. Grazing by wild horses and burros is one of these competing uses, and it arouses the animosity of interest groups that feel encroached upon. In particular, livestock groups consider that horses and burros compete with domestic animals for range forage; traditional wildlife advocates have the same concerns for indigenous wildlife; and other environmental groups con- sider equines to be aliens in ecosystems that have not evolved with, and are damaged by, them. On the other side there are equally strong advocates for wild horses and burros who consider these animals to be part of the western heritage and the aesthetic atmosphere of the region. Under existing law, it is the responsibility of the BLM and Forest Ser- vice to mediate these conflicting demands and to negotiate aggregate uses
vi PREFACE of the public lands among the interest groups. In areas with wild horses and burros, the compromises include decisions on the number of these animals that should be maintained along with the prescribed number of livestock and indigenous wildlife. All interest groups agree on one goal: the population of wild horses and burros, in conjunction with other wild and domestic grazing animals, should not be allowed to rise to levels at which the animals degrade the ecological health of rangelands. Hence, there is agreement that the aggregate numbers of wild horses and burros, livestock, and indigenous wildlife, and the spe- cific number decided upon for each class, should be controlled within the carrying capacity of each area. The BLM has adopted a policy stating that the management levelâtheir judgment of the appropriate numbersâfor wild horses on the public lands of the western United States should be 31,000. As of early 1990, this limit had not been reached; populations during the 1980s generally numbered between 40,000 and 50,000. Through yearly reproduction and a relative scarcity of natural population limiting factors in areas with healthy vegetation, wild horse and burro popu- lations increase at annual rates reportedly varying between 6 and 20 percent. Rates in the higher part of this range are more likely at low population densities and in areas where the range vegetation is in good to excellent condition. Thus, western populations of horses and burros increase several thousand each year. Given the unremitting tendency of these animals to increase, and deci- sions to hold horses and burros in each area at agreed-upon numbers, the management agencies face a continuing need to control population. P.L. 92-195 (U.S. Congress, 1971) states The Secretary may order wild free-roaming horses and burros to be destroyed in the most humane manner possible when he deems such action to be ... necessary to preserve and maintain the habitat in a suitable condition for continued use ... or such action is the only practical way to remove excess animals from the area. But the agencies have rejected mass euthanasia as a socially unacceptable solution and instead have developed the Adopt-a-Horse and Adopt-a-Burro programs. Periodic roundups of animals make those numbers in excess of management levels available for the general public to adopt as pets and work animals. The adoption program has been generally successful, placing 81,000 animals across the United States from 1972 through 1987 (U.S. Department of the Interior, 1989). However, it requires substantial funds, involving extensive helicopter time for roundups, high-quality pen facilities and feed to hold the animals until adoption, veterinary fees, and transportation costs to move
PREFACE Vll large numbers of animals across the country to adoption centers. It also places heavy demands on understaffed agencies that have numerous other natural resource management responsibilities across half the area of the western United States. Moreover, when the adoption demand is saturated, the agencies are faced with large and growing numbers of animals that need feed and shelter. This occurred during the mid-1980s when, after unusually large roundups, the BLM maintained several thousand wild horses in pens at Lovelock, Nevada, at an annual cost of several million dollars. In recent years, the BLM budget for wild horse and burro management has ranged between $10 million and $20 million annually. One alternative herd-control approach to roundup and adoption is repro- ductive suppression. In 1979, the National Research Council's Committee on Wild and Free-Roaming Horses and Burros was established under mandate of the Public Rangelands Improvement Act (P.L. 95-514) in part to design a wild horse and burro research program and to evaluate research funded by BLM (U.S. Congress, 1978). In 1980 this committee recommended an extensive research program that included studies on reproductive inhibition in mares. Five research projects were initiated in 1980, although none addressed fertility control. In 1982, the committee filed a final report (Na- tional Research Council, 1982). In 1983, all of the projects were terminated. In part because of growing concern with the cost of holding increasing numbers of unadopted horses in the Lovelock corrals, Congress appropriated $1 million in fiscal year 1985 for further research. The report accompany- ing the appropriations bill for the fiscal year 1985 budget of the U.S. Department of Interior stated (Robert F. Burford, U.S. Department of the Interior, per- sonal communication, November 20, 1984) [TJhere is still significant disagreement over how many animals are excess, what historic levels were, and what is the current level of reproduction. . . . [Thus we direct] the Bureau, through the National Academy of Sciences, to continue to develop data to answer these and other relevant questions. The Committee on Wild Horse and Burro Research was constituted in 1985 at the request of BLM and asked once again to consider research needs. BLM officials suggested a need for research on fertility control and computer simulation of alternative population control strategies. Upon committee recommendation, two projects were ultimately initiated and funded by BLM in 1985âone on fertility control and a related one on population genetics. The committee's final report summarizes its review of the research re- sults. The genetics study has been completed. The fertility control project has one more field season remaining as this report is written, but the data so far accrued have been extensively analyzed and modeled. When the modeling and remaining research have been completed in the fall of 1990, the fertility
viii PREFACE control project will provide not only a technical evaluation of the fertility control methodology used, but also an assessment of its population control efficiency and cost. BLM should then be in a position to compare the new methods with existing ones and to make policy decisions. Frederic H. Wagner, Chair Committee on Wild Horse and Burro Research
Contents 1 INTRODUCTION 1 2 RESEARCH AND RESULTS 3 Genetics Studies, 3 Mare Fertility Control Studies at Lovelock Corrals, 9 Mare Fertility Control Studies in the Field, 12 Vasectomy Experiments, 17 3 COMPUTER SIMULATION STUDIES 21 4 RESEARCH CONCERNS 23 Loss of the Clan Alpine Horses, 24 Collar Problems, 25 Foal Orphaning and Loss, 32 Abortion, 33 Disappearance of Penned Animals at Lovelock Corrals, 34 Food Chain Risks from Steroids, 35 5 CONCLUSIONS AND RECOMMENDATIONS 36 REFERENCES 38 APPENDIX BLM Report on Collared Horses, 41 IX.